Kubrick was quoted as saying: "I love editing. I think I like it more than any other phase of film making. If I wanted to be frivolous, I might say that everything that precedes editing is merely a way of producing film to edit."
Edward Dmytryk stipulates seven "rules of cutting" that a good editor should follow:
"Rule 1: Never make a cut without a positive reason."
"Rule 2: When undecided about the exact frame to cut on, cut long rather than short."
"Rule 3: Whenever possible cut 'in movement'."
"Rule 4: The 'fresh' is preferable to the 'stale'."
"Rule 5: All scenes should begin and end with continuing action."
"Rule 6: Cut for proper values rather than proper 'matches'."
"Rule 7: Substance first—then form."
According to Walter Murch, when it comes to film editing, there are six main criteria for evaluating a cut or deciding where to cut. They are (in order of importance, most important first, with notional percentage values.):
Emotion (51%) — Does the cut reflect what the editor believes the audience should be feeling at that moment?
Story (23%) — Does the cut advance the story?
Rhythm (10%) — Does the cut occur "at a moment that is rhythmically interesting and 'right'" (Murch, 18)?
Eye-trace (7%) — Does the cut pay respect to "the location and movement of the audience's focus of interest within the frame" (Murch, 18)?
Two-dimensional plane of the screen (5%) — Does the cut respect the 180 degree rule?
Three-dimensional space of action (4%) — Is the cut true to the physical/spatial relationships within the diegesis?
Murch assigned the notional percentage values to each of the criteria. "Emotion, at the top of the list, is the thing that you should try to preserve at all costs. If you find you have to sacrifice certain of those six things to make a cut, sacrifice your way up, item by item, from the bottom."-Murch
Some good documentaries on editing:
The Cutting Edge Magic of Movie Editing: http://www.youtube.com/watch?v=xJcQgQHR78Q
Some Good books:
1) The Technique of Film Editing- Karel Reisz and Gavin Miller- Focal Press
2) In the blink of an eye - Walter Murch